Sub-cooling a refrigerant in an air conditioning system

ABSTRACT

An air conditioning system includes a compressor configured to compress a refrigerant in a vapor phase; a condenser that receives the compressed vapor phase and is configured to change the compressed vapor phase to a liquid phase; an expansion device that receives the liquid phase of the refrigerant and is configured to expand the liquid phase of the refrigerant from a first pressure to a second pressure lower than the first pressure; an evaporator that receives the liquid phase of the refrigerant at the second pressure and is configured to transfer heat from an airflow circulated through the evaporator to the liquid phase of the refrigerant and change water vapor in the airflow into a liquid condensate; and a heat exchanger that receives at least a portion of the liquid phase of the refrigerant and is immersed in the liquid condensate to sub-cool the liquid phase of the refrigerant.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. § 119 to U.S. Provisional Patent Application No. 63/234,134, filed on Aug. 17, 2021, the entire contents of which are incorporated by reference herein.

TECHNICAL FIELD

This disclosure relates to sub-cooling a refrigerant in an air conditioning system and more particularly, sub-cooling a refrigerant in an air conditioning system with a condensate fluid.

BACKGROUND

Air conditioning systems often use a mechanical refrigeration cycle, such as a vapor-compression cycle to cool a fluid, such as an airflow. In some cases, a state of a refrigerant that is used as a working fluid affects an operational efficiency of the cooling system.

SUMMARY

This disclosure describes apparatus, systems, and methods for sub-cooling a refrigerant used in a mechanical refrigeration cycle.

In an example implementation, an air conditioning system includes at least one compressor configured to compress a refrigerant in a vapor phase; a condenser fluidly coupled to the at least one compressor to receive the compressed vapor phase of the refrigerant and configured to change the compressed vapor phase of the refrigerant to a liquid phase of the refrigerant by transferring heat from the compressed vapor phase of the refrigerant to a cooling fluid; an expansion device fluidly coupled to the condenser with a liquid line to receive the liquid phase of the refrigerant and configured to expand the liquid phase of the refrigerant from a first pressure to a second pressure lower than the first pressure; an evaporator fluidly coupled to the expansion device to receive the liquid phase of the refrigerant at the second pressure and configured to transfer heat from an airflow circulated through the evaporator to the liquid phase of the refrigerant at the second pressure to change at least a portion of the liquid phase of the refrigerant at the second pressure to the vapor phase of the refrigerant and change at least a portion of water vapor in the airflow into a liquid condensate; and a heat exchanger fluidly coupled to the liquid line to receive at least a portion of the liquid phase of the refrigerant from the condenser upstream of the expansion device. The heat exchanger is at least partially immersed in the liquid condensate captured in a condensate receiver from the evaporator and configured to sub-cool the portion of the liquid phase of the refrigerant based on a transfer of heat from the portion of the liquid phase of the refrigerant to the liquid condensate.

In an aspect combinable with the example implementation, the heat exchanger is integral with and part of the liquid line.

In another aspect combinable with any of the previous aspects, the heat exchanger includes a plurality of loops that are immersed in the liquid condensate captured in the condensate receiver from the evaporator.

In another aspect combinable with any of the previous aspects, the evaporator includes a cooling coil that includes a plurality of tubing rows, and the plurality of loops include a subset of the plurality of tubing rows.

In another aspect combinable with any of the previous aspects, the heat exchanger includes a shell-and-tube heat exchanger at least partially immersed in the liquid condensate captured in the condensate receiver from the evaporator.

In another aspect combinable with any of the previous aspects, the shell-and-tube heat exchanger includes a condensate inlet fluidly coupled to the liquid condensate in the condensate receiver; a condensate outlet fluidly coupled to an outlet of the condensate receiver; a liquid refrigerant inlet fluidly coupled to the condenser through the liquid line; and a liquid refrigerant outlet fluidly coupled to the expansion device through the liquid line.

Another aspect combinable with any of the previous aspects further includes a pump positioned to circulate liquid condensate to the shell-and-tube heat exchanger and through the condensate inlet.

In another aspect combinable with any of the previous aspects, the shell-and-tube heat exchanger includes a heat exchange surface configured to transfer heat from the liquid phase of the refrigerant to the liquid condensate.

In another aspect combinable with any of the previous aspects, the heat exchanger includes a liquid refrigerant inlet directly fluidly coupled to an outlet the condenser and a liquid refrigerant outlet directly coupled to an inlet of the expansion device.

Another aspect combinable with any of the previous aspects further includes a valve positioned in the liquid line between the liquid refrigerant inlet and the liquid refrigerant outlet.

In another aspect combinable with any of the previous aspects, the valve includes a solenoid valve.

In another aspect combinable with any of the previous aspects, the refrigerant includes a non-natural refrigerant.

In another aspect combinable with any of the previous aspects, the non-natural refrigerant includes at least one hydrofluorocarbon (HFC) refrigerant.

In another aspect combinable with any of the previous aspects, the at least one HFC refrigerant includes a blend of two or more HFC refrigerants.

In another aspect combinable with any of the previous aspects, the at least one HFC refrigerant includes at least one of HFC-134a, HFC-404a, HFC-410a, or HFC-407c.

In another aspect combinable with any of the previous aspects, the cooling fluid includes a cooling airflow circulated through the condenser by at least one fan to transfer heat from the vapor phase of the refrigerant to the cooling airflow.

In another aspect combinable with any of the previous aspects, the heat exchanger includes a liquid-to-liquid heat exchanger.

Another aspect combinable with any of the previous aspects further includes a liquid-to-air heat exchanger positioned to receive at least a portion of the airflow that exits the evaporator and the portion of the liquid phase of the refrigerant from the condenser upstream of the liquid-to-liquid heat exchanger.

In another aspect combinable with any of the previous aspects, the liquid-to-air heat exchanger is configured to transfer heat from the portion of the liquid phase of the refrigerant to the portion of the airflow that exits the evaporator.

In another aspect combinable with any of the previous aspects, the liquid-to-air heat exchanger includes a first liquid-to-air heat exchanger.

Another aspect combinable with any of the previous aspects further includes a second liquid-to-air heat exchanger positioned to receive at least a portion of the airflow that enters the evaporator and the portion of the liquid phase of the refrigerant from the first liquid-to-air heat exchanger upstream of the liquid-to-liquid heat exchanger.

In another aspect combinable with any of the previous aspects, the second liquid-to-air heat exchanger is configured to transfer additional heat from the portion of the liquid phase of the refrigerant to the portion of the airflow that enters the evaporator.

In another aspect combinable with any of the previous aspects, the heat exchanger includes a liquid-to-liquid heat exchanger, and the system further includes a liquid-to-air heat exchanger positioned to receive at least a portion of the airflow that enters the evaporator and the portion of the liquid phase of the refrigerant from the condenser upstream of the liquid-to-liquid heat exchanger. The liquid-to-air heat exchanger is configured to transfer heat from the portion of the liquid phase of the refrigerant to the portion of the airflow that enters the evaporator.

In another example implementation, a method for sub-cooling a refrigerant in an air conditioning system includes compressing a refrigerant in a vapor phase with at least one compressor; circulating the compressed vapor phase of the refrigerant from the at least one compressor to a condenser; changing the compressed vapor phase of the refrigerant to a liquid phase of the refrigerant in the condenser by transferring heat from the compressed vapor phase of the refrigerant to a cooling fluid; circulating at least a portion of the liquid phase of the refrigerant from the condenser through a liquid line to a heat exchanger that is at least partially immersed in a liquid condensate captured in a condensate receiver of an evaporator; sub-cooling the portion of the liquid phase of the refrigerant in the heat exchanger; circulating the sub-cooled portion of the liquid phase to an expansion device through the liquid line; expanding the liquid phase of the refrigerant from a first pressure to a second pressure lower than the first pressure in the expansion device; circulating the liquid phase of the refrigerant at the second pressure to the evaporator; and transferring heat from an airflow circulated through the evaporator to the liquid phase of the refrigerant at the second pressure to change at least a portion of the liquid phase of the refrigerant at the second pressure to the vapor phase of the refrigerant and change at least a portion of water vapor in the airflow into the liquid condensate.

In an aspect combinable with the example implementation, the heat exchanger is integral with and part of the liquid line.

Another aspect combinable with any of the previous aspects further includes circulating the portion of the liquid phase through a plurality of loops of the heat exchanger that are immersed in the liquid condensate captured in the condensate receiver from the evaporator.

In another aspect combinable with any of the previous aspects, the evaporator includes a cooling coil that includes a plurality of tubing rows, and the plurality of loops include a subset of the plurality of tubing rows.

Another aspect combinable with any of the previous aspects further includes circulating the portion of the liquid phase through a shell-and-tube heat exchanger at least partially immersed in the liquid condensate captured in the condensate receiver from the evaporator.

Another aspect combinable with any of the previous aspects further includes circulating liquid condensate from the condensate receiver through the shell-and-tube heat exchanger; transferring heat from the portion of the liquid phase of the refrigerant to the liquid condensate in the shell-and-tube heat exchanger to sub-cool the portion of the liquid phase of the refrigerant and heat the liquid condensate; circulating the sub-cooled portion of the liquid phase of the refrigerant through the liquid line to the expansion device from the shell-and-tube heat exchanger; and circulating the heated liquid condensate to a drain of the condensate receiver.

In another aspect combinable with any of the previous aspects, circulating liquid condensate from the condensate receiver through the shell-and-tube heat exchanger includes circulating liquid condensate from the condensate receiver through the shell-and-tube heat exchanger with a pump in or adjacent the condensate receiver.

Another aspect combinable with any of the previous aspects further includes circulating another portion of the liquid phase of the refrigerant through a valve positioned in the liquid line between the condenser and the expansion valve.

In another aspect combinable with any of the previous aspects, the valve includes a solenoid valve.

In another aspect combinable with any of the previous aspects, the refrigerant includes a non-natural refrigerant.

In another aspect combinable with any of the previous aspects, the non-natural refrigerant includes at least one hydrofluorocarbon (HFC) refrigerant.

In another aspect combinable with any of the previous aspects, the at least one HFC refrigerant includes a blend of two or more HFC refrigerants.

In another aspect combinable with any of the previous aspects, the at least one HFC refrigerant includes at least one of HFC-134a, HFC-404a, HFC-410a, or HFC-407c.

In another aspect combinable with any of the previous aspects, the cooling fluid includes a cooling airflow, and the method further includes circulating the cooling airflow through the condenser by at least one fan to transfer heat from the vapor phase of the refrigerant to the cooling airflow.

In another aspect combinable with any of the previous aspects, the heat exchanger includes a liquid-to-liquid heat exchanger, and the method further includes circulating the portion of the liquid phase of the refrigerant from the condenser to a liquid-to-air heat exchanger prior to circulating the portion of the liquid phase of the refrigerant to the liquid-to-liquid heat exchanger; circulating at least a portion of the airflow that exits the evaporator through the liquid-to-air heat exchanger; transferring heat from the portion of the liquid phase of the refrigerant to the portion of the airflow that exits the evaporator in the liquid-to-air heat exchanger; and circulating the cooled portion of the liquid phase of the refrigerant from the liquid-to-air heat exchanger to the liquid-to-liquid heat exchanger.

In another aspect combinable with any of the previous aspects, the liquid-to-air heat exchanger includes a first liquid-to-air heat exchanger, and the method further includes circulating the cooled portion of the liquid phase of the refrigerant from the first liquid-to-air heat exchanger to a second liquid-to-air heat exchanger prior to circulating the portion of the liquid phase of the refrigerant to the liquid-to-liquid heat exchanger; circulating at least a portion of the airflow that enters the evaporator through the second liquid-to-air heat exchanger; transferring heat from the cooled portion of the liquid phase of the refrigerant to the portion of the airflow that enters the evaporator in the second liquid-to-air heat exchanger; and circulating the further cooled portion of the liquid phase of the refrigerant from the second liquid-to-air heat exchanger to the liquid-to-liquid heat exchanger.

In another aspect combinable with any of the previous aspects, the heat exchanger includes a liquid-to-liquid heat exchanger, and the method further includes circulating at least a portion of the liquid phase of the refrigerant from the condenser to a liquid-to-air heat exchanger prior to circulating the portion of the liquid phase of the refrigerant to the liquid-to-liquid heat exchanger; circulating at least a portion of the airflow that enters the evaporator through the liquid-to-air heat exchanger; transferring heat from the portion of the liquid phase of the refrigerant to the portion of the airflow that enters the evaporator in the liquid-to-air heat exchanger; and circulating the cooled portion of the liquid phase of the refrigerant from the liquid-to-air heat exchanger to the liquid-to-liquid heat exchanger.

Implementations according to the present disclosure may include one or more of the following features. For example, air conditioning systems according to the present disclosure may provide for a higher coefficient of performance as compared to conventional systems. As another example, air conditioning systems according to the present disclosure may provide for a higher volumetric flow rate of a compressor in the system, thereby providing for decreased power use from the compressor. As another example, air conditioning systems according to the present disclosure may provide for such advantages without requiring any additional power-consuming components as compared to conventional systems.

The details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an example implementation of an air-conditioning system according to the present disclosure.

FIG. 2 is a schematic diagram of another example implementation of an air-conditioning system according to the present disclosure.

FIG. 3 is a schematic diagram of another example implementation of an air-conditioning system according to the present disclosure.

FIG. 4 is a schematic diagram of an example implementation of a refrigerant liquid-line coupled with a heat exchanger in an air-conditioning system according to the present disclosure.

FIG. 5 is a schematic diagram of another example implementation of a refrigerant liquid-line coupled with a heat exchanger in an air-conditioning system according to the present disclosure.

FIG. 6 is a flowchart that illustrates an example method for sub-cooling a refrigerant in an air-conditioning system according to the present disclosure.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram of an example implementation of an air conditioning system 100 according to the present disclosure. Generally, the air conditioning system 100 of FIG. 1 comprises a vapor-compression cycle system that utilizes a working fluid, such as a refrigerant fluid, to change the temperature of an airflow. The air conditioning system 100 includes the vapor-compression cycle components of a compressor 105, a condenser 110, a throttling device 115, and an evaporator 120. Although shown in FIG. 1 and described singularly, each of the vapor-compression cycle components can be one or more components (e.g., one or more compressors 105, one or more condensers 110, etc.). A refrigerant circulates through the vapor-compression cycle components of air conditioning system 100 and obtains and releases heat at different points in the cycle to ultimately change the temperature of an airflow. In an example implementation, the air conditioning system 100 comprises at least a part of a residential or commercial air conditioning system that can be used, e.g., to regulate a temperature of an indoor airflow to maintain an ambient temperature of indoor air in a residence or commercial space.

In the vapor-compression cycle of the air conditioning system 100, the compressor 105 (such as a reciprocating, scroll, or other compressor) uses, e.g., electrical power to compress a low pressure refrigerant vapor 102 to a higher pressure refrigerant vapor 104, with the specific pressures largely defined by the type of refrigerant used in the air conditioning system 100. For example, in some aspects, the refrigerant can be a chemical (i.e., not natural) refrigerant, such as a hydrofluorocarbon (HFC) refrigerant or a blend of HFC refrigerants. HFC refrigerants include, for example, HFC-134a, HFC-404a, HFC-410a, or HFC-407c. In some aspects, the air conditioning system 100 is designed to work with a chemical refrigerant exclusive of a natural refrigerant, such as ammonia or carbon dioxide. Generally, the vapor-compression cycle components of the air conditioning system 100 are designed to work optimally with a particular chemical refrigerant.

The high pressure refrigerant vapor 104 is at a higher pressure and temperature than the low pressure refrigerant vapor 102 taking into account the heat of compression added by the compressor 105. The high pressure refrigerant vapor 104 is circulated (e.g., naturally due to pressure difference) to the condenser 110. The condenser 110, generally, comprises a single or multi-circuit heat exchanger (e.g., fin and tube or otherwise) that also receives a separate flow of a cooling fluid 106 (e.g., air, water, or other fluid). The condenser 110, as a heat exchanger, facilitates heat transfer from the high pressure refrigerant vapor 104 to the cooling fluid 106 to condense all or part of the high pressure refrigerant vapor 104 to a refrigerant liquid 107 (also called a liquid line 107 in the present disclosure). The cooling fluid 106 exits the condenser 110 as a warmer cooling fluid 108 (e.g., as circulated through the condenser 110 with one or more fans or pumps, as appropriate for the particular fluid).

The refrigerant liquid 107, in this example implementation, is circulated from the condenser 110 to a heat exchanger 112 (e.g., a liquid-to-liquid heat exchanger) that is positioned in a condensate pan 130 that is positioned to capture liquid condensate 114 from the evaporator 120. In some aspects, the heat exchanger 112 is submerged (all or substantially) in the condensate 114 that is captured, at least transiently, in the condensate pan 130. Condensate 114 exits the condensate pan 130 at port 116 as condensate flow 118.

Refrigerant liquid 107 transfers heat, via heat exchanger 112, to the condensate 114, which is at a substantially lower temperature than the refrigerant liquid 107 (which, upon leaving the condenser 110, is at the same or substantially same temperature as the refrigerant vapor 104). The condensate 114 that is captured in the condensate pan 130 flows from the evaporator 120 (e.g., as an air-to-liquid heat exchanger, or “cooling coil”) and results from condensation of water vapor from a warm (return) airflow 124 that is circulated (e.g., by one or more fans, not shown) through the evaporator 120. The warm (return) airflow 124, circulated through the evaporator 120, exits the evaporator 120 as cooled (supply) airflow 126 after transferring heat, via the evaporator 120, to refrigerant supply 121 that is circulated to the evaporator 120.

As shown in FIG. 1 , sub-cooled refrigerant liquid 109 exits the heat exchanger 112 and is circulated to the throttling device 115. In some aspects, the throttling device 115 is an adjustable valve, such as a thermal expansion valve (TXV). The throttling device 115, as a TXV, is controllably adjusted (open or closed) to control an amount (e.g., volumetric flow rate) of the refrigerant supply 121 from the throttling device 115 to the evaporator 120. In this example, the throttling device 115 is controlled to open (to allow more refrigerant supply 121 to flow to the evaporator 120) or close (to allow less refrigerant supply 121 to flow to the evaporator 120) by a pressure bulb 125 that is mounted to a refrigerant return 102 that exists the evaporator 120 and enters the compressor 105. In this example of the throttling device 115 as a TXV, the pressure bulb 125 measures a temperature of the refrigerant in the refrigerant return 102 (to measure refrigerant super heat) and controls (e.g., through a pressure force in pressure line 122) the TXV.

As the sub-cooled refrigerant 109 passes through the throttling device 115, the sub-cooled refrigerant 109 (which is below the boiling point for the refrigerant) is in a complete liquid state for the refrigerant. The throttling device 115 changes the sub-cooled refrigerant 109 from a warm, liquid state, to a cold, liquid state through a pressure drop initiated by the flow of the sub-cooled refrigerant 109 through the throttling device 115 into the refrigerant supply 121.

The refrigerant supply 121 enters the evaporator 120 and, through heat transfer from the warm airflow 124 in the evaporator 120, evaporates all or part of the (cold) refrigerant supply 121 into the refrigerant return 102 (which is at a vapor or multiphase state). As described, the pressure bulb 125 measures the degree of superheat of the refrigerant return 102 to control the throttling device 115.

In some aspects, the heat exchanger 112 provides for a more dense liquid (sub-cooled refrigerant 109) to enter the throttling device 115 compared to if, for example, the refrigerant liquid 107 was provided directly to the throttling device 115 from the condenser 110. As a more dense liquid refrigerant, expansion of the sub-cooled refrigerant 109 is enhanced through the throttling device 115 (and subsequently the evaporator 120). In some aspects, this can result in throttling (e.g., closing) of the throttling device 115 (either mechanical as a TXV or electronic) since less refrigerant supply 121 will be to achieve the same (or very similar) amount of heat transfer from the warm airflow 124 into the refrigerant supply 121 in the evaporator 120. In some aspects, such a result can also provide the benefit of slowing down a variable speed compressor (as compressor 105) to maintain volumetric efficiency, which can reduce electrical power consumption by the compressor 105. Thus, a net increase to an energy efficiency ratio (EER) of cooling power (in BTUs) to power consumption (in watts) or a seasonal energy efficiency ratio (SEER) of cooling power (in BTUs) to power consumption (in watts) can vary but could be an increase as much as 25% over convention air conditioning systems. Further, in hotter and more humid climes, such ratios can be more improved due to, for example, a more constant flow of condensate 114 (due to the higher humidity ratio of the warm airflow 124).

FIG. 2 is a schematic diagram of another example implementation of an air-conditioning system 200 according to the present disclosure. In some aspects, air conditioning system 200 is similar to air conditioning system 100 but also includes valve 225, which can modulate a supply of refrigerant liquid between a heat exchanger and a throttling device in the air conditioning system 200. For example, like air conditioning system 100, the air conditioning system 200 of FIG. 2 comprises a vapor-compression cycle system that utilizes a working fluid, such as a refrigerant fluid, to change the temperature of an airflow. The air conditioning system 200 includes the vapor-compression cycle components of a compressor 205, a condenser 210, a throttling device 215, and an evaporator 220. Although shown in FIG. 2 and described singularly, each of the vapor-compression cycle components can be one or more components (e.g., one or more compressors 205, one or more condensers 210, etc.). A refrigerant circulates through the vapor-compression cycle components of air conditioning system 200 and obtains and releases heat at different points in the cycle to ultimately change the temperature of an airflow. In an example implementation, the air conditioning system 200 comprises at least a part of a residential air conditioning system that can be used, e.g., to regulate a temperature of an indoor airflow to maintain an ambient temperature of indoor air in a residence.

In the vapor-compression cycle of the air conditioning system 200, the compressor 205 (such as a reciprocating, scroll, or other compressor) uses, e.g., electrical power to compress a low pressure refrigerant vapor 202 (refrigerant return) to a higher pressure refrigerant vapor 204, with the specific pressures largely defined by the type of refrigerant used in the air conditioning system 200. For example, in some aspects, the refrigerant can be a chemical (i.e., not natural) refrigerant, such as a hydrofluorocarbon (HFC) refrigerant or a blend of HFC refrigerants. HFC refrigerants include, for example, HFC-134a, HFC-404a, HFC-410a, or HFC-407c. In some aspects, the air conditioning system 200 is designed to work with a chemical refrigerant exclusive of a natural refrigerant, such as ammonia or carbon dioxide. Generally, the vapor-compression cycle components of the air conditioning system 200 are designed to work optimally with a particular chemical refrigerant.

The high pressure refrigerant vapor 204 is at a higher pressure and temperature than the low pressure refrigerant vapor 202 taking into account the heat of compression added by the compressor 205. The high pressure refrigerant vapor 204 is circulated (e.g., naturally due to pressure difference) to the condenser 210. The condenser 210, generally, comprises a single or multi-circuit heat exchanger (e.g., fin and tube or otherwise) that also receives a separate flow of a cooling fluid 206 (e.g., air, water, or other fluid). The condenser 210, as a heat exchanger, facilitates heat transfer from the high pressure refrigerant vapor 204 to the cooling fluid 206 to condense all or part of the high pressure refrigerant vapor 204 to a refrigerant liquid 207 (also called a liquid line 207 in the present disclosure). The cooling fluid 206 exits the condenser 210 as a warmer cooling fluid 208 (e.g., as circulated through the condenser 210 with one or more fans or pumps, as appropriate for the particular fluid).

The refrigerant liquid 207, in this example implementation, is circulated from the condenser 210 to either a heat exchanger 212 (e.g., a liquid-to-liquid heat exchanger) that is positioned in a condensate pan 230 that is positioned to capture liquid condensate 214 from the evaporator 220 or to a throttling device 215 as controlled by the valve 225. In some aspects, the valve 225 is or includes a solenoid valve 225. In some aspects, the valve 225 controls an amount of the refrigerant liquid 211 that flows to the heat exchanger 212 (e.g., from 0-100%) and an amount of the refrigerant liquid 211 that flows to the throttling device (e.g., from 0-100%). For example, in some aspects, air conditioning system 200 may be a heat pump system (with the addition of an appropriate reversing valve) and the valve 225 is closed during cooling operation (to allow refrigerant liquid 211 to flow to the heat exchanger 212 from the condenser 210) and open during heating operation (to allow refrigerant liquid to flow from the throttling device 215 to the condenser 210).

In some aspects, the heat exchanger 212 is submerged (all or substantially) in the condensate 214 that is captured, at least transiently, in the condensate pan 230. Condensate 214 exits the condensate pan 230 at port 216 as condensate flow 218. Refrigerant liquid 207 transfers heat, via heat exchanger 212, to the condensate 214, which is at a substantially lower temperature than the refrigerant liquid 207 (which, upon leaving the condenser 210, is at the same or substantially same temperature as the refrigerant vapor 204). The condensate 214 that is captured in the condensate pan 230 flows from the evaporator 220 (e.g., as an air-to-liquid heat exchanger, or “cooling coil”) and results from condensation of water vapor from a warm (return) airflow 224 that is circulated (e.g., by one or more fans, not shown) through the evaporator 220. The warm (return) airflow 224, circulated through the evaporator 220, exits the evaporator 230 as cooled (supply) airflow 226 after transferring heat, via the evaporator 220, to refrigerant supply 221 that is circulated to the evaporator 220.

As shown in FIG. 2 , sub-cooled refrigerant liquid 209 exits the heat exchanger 212 and is circulated to the throttling device 215 (without entering a bypass line that includes the valve 225). In some aspects, the throttling device 215 is an adjustable valve, such as a thermal expansion valve (TXV). The throttling device 215, as a TXV, is controllably adjusted (open or closed) to control an amount (e.g., volumetric flow rate) of the refrigerant supply 221 from the throttling device 215 to the evaporator 220. In this example, the throttling device 215 is controlled to open (to allow more refrigerant supply 221 to flow to the evaporator 220) or close (to allow less refrigerant supply 221 to flow to the evaporator 220) by a pressure bulb 227 that is mounted to a refrigerant return 202 that exists the evaporator 220 and enters the compressor 205. In this example of the throttling device 215 as a TXV, the pressure bulb 227 measures a temperature of the refrigerant in the refrigerant return 202 (to measure refrigerant super heat) and controls (e.g., through a pressure force in pressure line 222) the TXV.

As the sub-cooled refrigerant 209 passes through the throttling device 215, the sub-cooled refrigerant 209 (which is below the boiling point for the refrigerant) is in a complete liquid state for the refrigerant. The throttling device 215 changes the sub-cooled refrigerant 209 from a warm, liquid state, to a cold, liquid state through a pressure drop initiated by the flow of the sub-cooled refrigerant 209 through the throttling device 215 into the refrigerant supply 221.

The refrigerant supply 221 enters the evaporator 220 and, through heat transfer from the warm airflow 224 in the evaporator 220, evaporates all or part of the (cold) refrigerant supply 221 into the refrigerant return 202 (which is at a vapor or multiphase state). As described, the pressure bulb 227 measures the degree of superheat of the refrigerant return 202 to control the throttling device 215.

As with the air conditioning system 100, in some aspects, the heat exchanger 212 provides for a more dense liquid (sub-cooled refrigerant 209) to enter the throttling device 215 compared to if, for example, the refrigerant liquid 207 was provided directly to the throttling device 215 from the condenser 210. As a more dense liquid refrigerant, expansion of the sub-cooled refrigerant 209 is enhanced through the throttling device 215 (and subsequently the evaporator 220). In some aspects, this can result in throttling (e.g., closing) of the throttling device 215 (either mechanical as a TXV or electronic) since less refrigerant supply 221 will be to achieve the same (or very similar) amount of heat transfer from the warm airflow 224 into the refrigerant supply 221 in the evaporator 220. In some aspects, such a result can also provide the benefit of slowing down a variable speed compressor (as compressor 205) to maintain volumetric efficiency, which can reduce electrical power consumption by the compressor 205. Thus, a net increase to an energy efficiency ratio (EER) of cooling power (in BTUs) to power consumption (in watts) or a seasonal energy efficiency ratio (SEER) of cooling power (in BTUs) to power consumption (in watts) can vary but could be an increase as much as 25% over convention air conditioning systems. Further, in hotter and more humid climes, such ratios can be more improved due to, for example, a more constant flow of condensate 214 (due to the higher humidity ratio of the warm airflow 224).

FIG. 3 is a schematic diagram of another example implementation of an air-conditioning system 300 according to the present disclosure. In some aspects, air conditioning system 300 is similar to air conditioning systems 100 and 200 but also includes one or more additional liquid-to-air heat exchangers through which a liquid refrigerant flows prior to entering a liquid-to-liquid heat exchanger. For example, like air conditioning systems 100 and 200, the air conditioning system 300 of FIG. 3 comprises a vapor-compression cycle system that utilizes a working fluid, such as a refrigerant fluid, to change the temperature of an airflow. The air conditioning system 300 includes the vapor-compression cycle components of a compressor 305, a condenser 310, a throttling device 315, and an evaporator 320. Although shown in FIG. 3 and described singularly, each of the vapor-compression cycle components can be one or more components (e.g., one or more compressors 305, one or more condensers 310, etc.). A refrigerant circulates through the vapor-compression cycle components of air conditioning system 300 and obtains and releases heat at different points in the cycle to ultimately change the temperature of an airflow. In an example implementation, the air conditioning system 300 comprises at least a part of a residential air conditioning system that can be used, e.g., to regulate a temperature of an indoor airflow to maintain an ambient temperature of indoor air in a residence.

In the vapor-compression cycle of the air conditioning system 300, the compressor 305 (such as a reciprocating, scroll, or other compressor) uses, e.g., electrical power to compress a low pressure refrigerant vapor 302 to a higher pressure refrigerant vapor 304, with the specific pressures largely defined by the type of refrigerant used in the air conditioning system 300. For example, in some aspects, the refrigerant can be a chemical (i.e., not natural) refrigerant, such as a hydrofluorocarbon (HFC) refrigerant or a blend of HFC refrigerants. HFC refrigerants include, for example, HFC-134a, HFC-404a, HFC-410a, or HFC-407c. In some aspects, the air conditioning system 300 is designed to work with a chemical refrigerant exclusive of a natural refrigerant, such as ammonia or carbon dioxide. Generally, the vapor-compression cycle components of the air conditioning system 300 are designed to work optimally with a particular chemical refrigerant.

The high pressure refrigerant vapor 304 is at a higher pressure and temperature than the low pressure refrigerant vapor 302 taking into account the heat of compression added by the compressor 305. The high pressure refrigerant vapor 304 is circulated (e.g., naturally due to pressure difference) to the condenser 310. The condenser 310, generally, comprises a single or multi-circuit heat exchanger (e.g., fin and tube or otherwise) that also receives a separate flow of a cooling fluid 306 (e.g., air, water, or other fluid). The condenser 310, as a heat exchanger, facilitates heat transfer from the high pressure refrigerant vapor 304 to the cooling fluid 306 to condense all or part of the high pressure refrigerant vapor 304 to a refrigerant liquid 307 (also called a liquid line 307 in the present disclosure). The cooling fluid 306 exits the condenser 310 as a warmer cooling fluid 308 (e.g., as circulated through the condenser 310 with one or more fans or pumps, as appropriate for the particular fluid).

The refrigerant liquid 307, in this example implementation, is circulated from the condenser 310 to a pre-cooler 328 (e.g., a liquid-to-air heat exchanger) that is positioned to receive a warm (return) airflow 326 that enters the evaporator 320. In this example, heat from the refrigerant liquid 307 is transferred to the warm (return) airflow 326, thereby, e.g., further warming the warm (return) airflow 326 in the pre-cooler 328. Further, by transferring heat, the refrigerant liquid 307 is further cooled from when it exits the condenser 310 (e.g., thereby further condensing any vapor left). In some aspects, use of the pre-cooler 328 may prevent or help prevent freezing of the evaporator 320 by, e.g., heating the warm (return) airflow 326 that enters the evaporator 320.

In this example implementation, cooled refrigerant liquid 332 exits the pre-cooler 328 and enters a pre-cooler 330 (e.g., a liquid-to-air heat exchanger) that is positioned to receive a cooled (supply) airflow 324 that exits the evaporator 320. In this example, heat from the cooled refrigerant liquid 332 is further transferred to the cooled (supply) airflow 324, thereby, e.g., dehumidifying the cooled (supply) airflow 324 in the pre-cooler 330. Further, by transferring heat, the cooled refrigerant liquid 332 is further cooled from when it exits the pre-cooler 328 (e.g., thereby further condensing any vapor).

In this example implementation, both the pre-cooler 328 and pre-cooler 330 are used in the air conditioning system 300. In alternative implementations, such as in humid climates, only the pre-cooler 330 can be used in the air conditioning system 300. In other alternative implementations, only the pre-cooler 330 can be used in the air conditioning system 300. In some aspects, both the pre-cooler 328 and pre-cooler 330 are provided in the air conditioning system 300 but refrigerant is selectively circulated to one or the other based on, e.g., a mode of operation of the air conditioning system 300 or ambient conditions.

As shown in FIG. 3 , one or more valves (such as solenoid valves), each illustrated as an encircled “X,” and one or more bypass conduits in which the valves, can be positioned in the air conditioning system 300 to allow for selective circulation of the refrigerant liquid 307 to one or both of the pre-cooler 328 and pre-cooler 330. For example, one or more solenoid valves can be positioned to isolate (i.e., fluidly decouple from the refrigerant liquid 307) the pre-cooler 330 (e.g., if dehumidification is not needed) or to isolate pre-cooler 328 (e.g., if coil temperature such as by a freeze stat indicates that freeze prevention is needed). For example, the illustrated valves can be operated (e.g., to open or close) to allow refrigerant liquid 307 to bypass both the pre-cooler 328 and the pre-cooler 330, only the pre-cooler 328, only the pre-cooler 330, or neither of the pre-cooler 328 and the pre-cooler 330.

As shown in FIG. 3 , a further cooled refrigerant liquid 334 is circulated to a heat exchanger 312 (e.g., a liquid-to-liquid heat exchanger) that is positioned in a condensate pan 331 that is positioned to capture liquid condensate 314 from the evaporator 320. In some aspects, the heat exchanger 312 is submerged (all or substantially) in the condensate 314 that is captured, at least transiently, in the condensate pan 331. Condensate 314 exits the condensate pan 331 at port 316 as condensate flow 318. Further cooled refrigerant liquid 334 transfers heat, via heat exchanger 312, to the condensate 314, which is at a substantially lower temperature than the further cooled refrigerant liquid 334. The condensate 314 that is captured in the condensate pan 331 flows from the evaporator 320 (e.g., as an air to liquid heat exchanger, or “cooling coil”) and results from condensation of water vapor from a warm airflow 324 that is circulated (e.g., by one or more fans, not shown) through the evaporator 320. The warm airflow 324, circulated through the evaporator 320, exits the evaporator 320 as cooled airflow 326 after transferring heat, via the evaporator 320, to further cooled refrigerant liquid 334 that is circulated to the evaporator 320.

As shown in FIG. 3 , sub-cooled refrigerant liquid 336 exits the heat exchanger 312 and is circulated to the throttling device 315. In some aspects, the throttling device 315 is an adjustable valve, such as a thermal expansion valve (TXV). The throttling device 315, as a TXV, is controllably adjusted (open or closed) to control an amount (e.g., volumetric flow rate) of the refrigerant supply 321 from the throttling device 315 to the evaporator 320. In this example, the throttling device 315 is controlled to open (to allow more refrigerant supply 321 to flow to the evaporator 320) or close (to allow less refrigerant supply 321 to flow to the evaporator 320) by a pressure bulb 325 that is mounted to a refrigerant return 302 that exists the evaporator 320 and enters the compressor 305. In this example of the throttling device 315 as a TXV, the pressure bulb 325 measures a temperature of the refrigerant in the refrigerant return 302 (to measure refrigerant super heat) and controls (e.g., through a pressure force in pressure line 322) the TXV. Although not shown in FIG. 3 , a valve such as valve 225 in FIG. 2 can be installed in a bypass conduit between the refrigerant liquid 307 and the sub-cooled refrigerant liquid 336 in order to controllably bypass refrigerant liquid 307 directly to the throttling device without passing through the heat exchanger 312 (or the pre-coolers 328 and 330).

As the sub-cooled refrigerant 336 passes through the throttling device 315, the sub-cooled refrigerant 336 (which is below the boiling point for the refrigerant) is in a complete liquid state for the refrigerant. The throttling device 315 changes the sub-cooled refrigerant 336 from a warm, liquid state, to a cold, liquid state through a pressure drop initiated by the flow of the sub-cooled refrigerant 336 through the throttling device 315 into the refrigerant supply 321.

The refrigerant supply 321 enters the evaporator 320 and, through heat transfer from the warm airflow 324 in the evaporator 320, evaporates all or part of the (cold) refrigerant supply 321 into the refrigerant return 302 (which is at a vapor or multiphase state). As described, the pressure bulb 325 measures the degree of superheat of the refrigerant return 302 to control the throttling device 315.

As with the air conditioning systems 100 and 200, in some aspects, the heat exchanger 312 provides for a more dense liquid (sub-cooled refrigerant 336) to enter the throttling device 315 compared to if, for example, the refrigerant liquid 307 was provided directly to the throttling device 315 from the condenser 310. As a more dense liquid refrigerant, expansion of the sub-cooled refrigerant 336 is enhanced through the throttling device 315 (and subsequently the evaporator 320). In some aspects, this can result in throttling (e.g., closing) of the throttling device 315 (either mechanical as a TXV or electronic) since less refrigerant supply 321 will be to achieve the same (or very similar) amount of heat transfer from the warm airflow 324 into the refrigerant supply 321 in the evaporator 320. In some aspects, such a result can also provide the benefit of slowing down a variable speed compressor (as compressor 305) to maintain volumetric efficiency, which can reduce electrical power consumption by the compressor 305. Thus, a net increase to an energy efficiency ratio (EER) of cooling power (in BTUs) to power consumption (in watts) or a seasonal energy efficiency ratio (SEER) of cooling power (in BTUs) to power consumption (in watts) can vary but could be an increase as much as 25% over convention air conditioning systems. Further, in hotter and more humid climes, such ratios can be more improved due to, for example, a more constant flow of condensate 314 (due to the higher humidity ratio of the warm airflow 324).

In the example implementation of the air conditioning system 300 (and, in some aspects, also for the air conditioning system 100 and air conditioning system 200), the following example temperatures can be achieved during operation. For example, the high pressure refrigerant vapor 304 can leave leaving the condenser 310 between 144-160° F. The refrigerant liquid 307 (as well as refrigerant liquid 107 and 207) can exit the condenser 310 at between 90-112° F. (including a 25-40° F. drop in the main condenser bundle and another 8° F. drop in the sub-cooler condenser bundle). Warm (return) airflow 326 can enter the evaporator 320 at between 73-80° F. (with a similar temperature range for warm airflows 124 and 224). Cooled (supply) airflow 324 can leave the evaporator 320 at between 50-57° F. (with a similar temperature range for cooled airflows 126 and 226). The condensate 314 can be between 38-48° F. (with a similar temperature range for condensates 114 and 214). Thus, a refrigerant liquid that circulates through a liquid-to-liquid heat exchanger positioned in the condensate according to the present disclosure can drop about 15° F. through heat exchange with the cold condensate. In the case of air conditioning system 300, the refrigerant liquid can drop about 5° F. by passing through pre-cooler 328. The refrigerant liquid can further drop an additional 10° F. by passing through pre-cooler 330.

Thus, in the case of the air conditioning system 300, a total temperature drop of the refrigerant liquid between the condenser 310 and the throttling device 315 can be about 30° F. By reducing the temperature as such, additional cooling capacity is possible through the normal operation of the throttling device 315. For example, conventional TXVs use correction factors for nominal capacity of the valve (which limits nominal capacity of the air conditioning system generally) according to the temperature of the refrigerant liquid that enters the TXV. A temperature of 100° F. for the refrigerant liquid corresponds to a correction factor of 1.0, meaning that the nominal capacity is based on a refrigerant liquid temperature of 100° F. entering the TXV. However, for an entering refrigerant liquid temperature of 70° F., the correction factor can be between 1.17-1.33 (depending on refrigerant). Thus, an entering refrigerant liquid temperature of 70° F. in the air conditioning system 300 can provide for between a 17% and 33% increase in cooling capacity (depending on refrigerant type) for the TXV (and thus, the air conditioning system all other factors being equal) (see Sporlan Catalog 201, May 2011, at pages 4-8). Other increased capacities can be had by using the air conditioning system 100 or 200 simply with the temperature drop (of about 15° F.) through the heat exchanger 112 or 212, respectively. The increased capacity of the TXV results in a better Coefficient of Performance (COP). The end result is to achieve the same work (cooling tonnage) while allowing the compressor to operate at a lower volume, thereby resulting in a better volumetric efficiency of the compressor (the main electrical power user of the vapor-compression cycle components).

Generally, each of air conditioning systems 100, 200, and 300 can take the form of a split-system air conditioning system or a packaged unit air conditioning system, which are both contemplated by the present disclosure. For example, as a split-system air conditioning system, the one or more compressors and one or more condensers can be placed or housed in a common unit (generally, a condensing unit that is located outdoors), while the one or more evaporators, as well as the throttling device, can be placed or housed in another common unit (generally, a furnace, air handler, or fan coil unit located indoors). In some aspects, the throttling device can be external to such a common unit but mounted adjacent thereto. This common unit may also include one or more fans (that circulates the described airflows), as well as other components, such as air filters, UV lights, heating devices, or otherwise.

As a packaged unit, all of the vapor compression cycle components, as well as fans, air filters, UV lights, and/or heating devices, can be mounted in a single, common unit. This single, common unit generally sits outside of the indoor space to be conditioned, such as on a roof or aside a building that encloses the indoor space. Thus, in the case of a packaged unit, only airflows (supply and return) may be communicated between the packaged unit in the outdoor space and the indoor space to be conditioned.

FIG. 4 is a schematic diagram of an example implementation of a refrigerant liquid-line coupled with a heat exchanger in an air-conditioning system according to the present disclosure. For example, FIG. 4 shows an example implementation of air conditioning system 100, but could also be applied to the implementations of air conditioning system 200 or air conditioning system 300. In this figure, the heat exchanger 112 comprises a looped, liquid-to-liquid heat exchanger that includes one or more (in this example, three) loop sections 111 that are fluidly coupled together and between the refrigerant liquid 107 (liquid line 107) and the sub-cooled refrigerant liquid 109. As shown in FIG. 4 , the loop sections 111 can be submerged (completely or substantially) within the condensate 114 in the condensate pan 130. Generally, a number of the loop sections 111 can determine an amount of heat transferred from the refrigerant liquid 107 into the condensate 114, i.e., the more loop sections 111 the greater the heat transfer. In operation refrigerant liquid from the condenser 110 circulated through the loop sections 111 in the heat exchanger 112 to transfer heat to the condensate 114.

In some aspects, the loop sections 111 are arranged vertically within a depth of the condensate pan 130 such that refrigerant liquid 107 enters the heat exchanger 112 at a loop section 111 near the top level of the condensate 114 and exits the heat exchanger 112 at a loop section 111 near the bottom level of the condensate 114 in the condensate pan 130. Thus, the warmest refrigerant liquid 107 exchanges heat with the warmest condensate 114, while the coldest refrigerant liquid 107 exchanges heat with the coldest condensate 114 (i.e., in a counter flow arrangement). Such an arrangement can also be used in air conditioning system 200 and air conditioning system 300.

In some aspects, the loop sections 111 are integral with, but fluidly decoupled from, one or more rows of a cooling coil that is part of the evaporator 120. For example, for ease of manufacturing, one or more bottom rows of the cooling coil can comprise the heat exchanger 112 that sits in the condenser 114 (and through which no airflow passes), while the remaining rows of the cooling coil (through which airflow passes) sit above the condensate pan 130. The one or more bottom rows of the cooling coil that comprise the heat exchanger 112 include a separate inlet (for the refrigerant liquid 107) and a separate outlet (for the sub-cooled refrigerant 109) as compared to the inlet (for refrigerant supply 121) and the outlet (for low pressure refrigerant vapor 102) of the cooling coil through which warm (return) airflow 124 passes (and is cooled into supply airflow 126).

In some aspects, the loop section 111 can also include one or more heat exchange plates (e.g., aluminum or copper plates) connected to the loop sections 111 to increase heat transfer from the refrigerant liquid 107 to the condensate 114. As another example, the heat exchanger 112 can take the form of a spiral copper in a vertical pipe (e.g., in a counter flow arrangement).

FIG. 5 is a schematic diagram of another example implementation of a refrigerant liquid-line coupled with a heat exchanger in an air-conditioning system according to the present disclosure. For example, FIG. 5 shows an example implementation of air conditioning system 100, but could also be applied to the implementations of air conditioning system 200 or air conditioning system 300. In this figure, the heat exchanger 112 comprises, for example, a plate and frame, welded/brazed plate, or shell and tube heat exchanger that thermally couples the refrigerant liquid 107 with the condensate 114 without mixing the refrigerant and condensate. In some aspects, the condensate 114 can flow naturally into the heat exchanger 112 as an input flow 117 and flow out of the heat exchanger 112 as an output flow 119. As shown in FIG. 5 , however, in some aspects, a pump 113 may provide forced circulation of the input flow 117 of the condensate 114 into the heat exchanger 112 and out of the heat exchanger 112 as output flow 119. The design of a heat exchange surface (e.g., number of plates, number of fins, materials, number of tubes in a shell) of the heat exchanger 112 can determine an amount of heat transferred from the refrigerant liquid 107 into the condensate 114. In operation, refrigerant liquid from the condenser 110 circulates through the heat exchanger 112 to transfer heat to the condensate 114 that is also circulated through the heat exchanger 112 (e.g., in a counter flow arrangement).

FIG. 6 is a flowchart that illustrates an example method 600 for sub-cooling a refrigerant in an air-conditioning system. In some aspects, method 600 can be performed with or by any of the air conditioning systems 100, 200, or 300, or other air conditioning systems according to the present disclosure. Method 600 can begin at step 602, which includes compressing a refrigerant in a vapor phase with at least one compressor. For example, using air conditioning system 100 as an example, the compressor 105 compresses the low pressure refrigerant vapor 102 into high pressure refrigerant vapor 104 and also adds heat of compression to raise the temperature of the refrigerant vapor (beyond the temperature rise due to pressure rise).

Method 600 can continue at step 604, which includes circulating the vapor phase of the refrigerant from the at least one compressor to a condenser. For example, continuing the example of air conditioning system 100, the high pressure refrigerant vapor 104 is circulated from the compressor 105 to the condenser 110.

Method 600 can continue at step 606, which includes changing the vapor phase of the refrigerant to a liquid phase of the refrigerant in the condenser by transferring heat from the vapor phase of the refrigerant to a cooling fluid. For example, continuing the example of air conditioning system 100, high pressure refrigerant vapor 104 is condensed into refrigerant liquid 107 via the condenser 110 and heat transfer from the refrigerant to a cooling fluid 106. Cooling fluid 106, in some aspects, can be a cooling airflow that is circulated through the condenser 110 by one or more fans (typically that are part of the condenser 110). The heat from the refrigerant vapor 104 causes a temperature rise of the cooling fluid 106 into a warmed fluid 108 (e.g., warmer airflow). Thus, in this example, phase change (but not an appreciable temperature change) of the refrigerant (from vapor 104 to liquid 107) in the condenser 110.

Method 600 can continue at step 608, which includes circulating at least a portion of the liquid phase of the refrigerant from the condenser through a liquid line to a heat exchanger that is at least partially immersed in a liquid condensate captured in a condensate receiver of an evaporator. For example, continuing the example of air conditioning system 100, refrigerant liquid 107 (within a conduit, such as a copper tubing, and also called liquid line 107) circulates from the condenser 110 to the heat exchanger 112 that is immersed in the condensate 114. The condensate 114 is captured (at least transiently before it drains) in the condensate pan 130 and comprises condensed water vapor from an airflow that is cooled through the evaporator 120.

With reference to air conditioning system 200, in some aspects, step 608 can include circulating a portion of the refrigerant liquid 207 into the heat exchanger 212 while another portion is circulated through the valve 225 directly from the condenser 210 to the throttling device 215. Thus, in the example of air conditioning system 200, all of the refrigerant liquid 207 can be circulated from the condenser 210 to the heat exchanger 212, all of the refrigerant liquid 207 can be circulated from the condenser 210 to the throttling device 215, or portions of the refrigerant liquid 207 can be circulated from the condenser 210 to the heat exchanger 212 and throttling device 215, respectively, by operation of the valve 225. Then sub-cooled refrigerant liquid 209 and refrigerant liquid 207 can then mix prior to entering the throttling device 215.

With reference to air conditioning system 300, in some aspects, prior to step 608, the refrigerant liquid 307 can be circulated to one or both pre-coolers 328 or 330 prior to circulating to the heat exchanger 312. Thus, in that example, the refrigerant liquid 307 can be precooled by airflows that enter and/or exit the evaporator 320 before being sub-cooled in the heat exchanger 312.

Method 600 can continue at step 610, which includes sub-cooling the portion of the liquid phase of the refrigerant in the heat exchanger. For example, continuing the example of air conditioning system 100, as the refrigerant liquid 107 passes through the heat exchanger 112, heat is transferred from the refrigerant liquid 107 into the condensate 114. In some aspects, the temperature drop of the refrigerant liquid 107 can be about 15° F. (with higher temperature drops occurring, for example, in air conditioning system 300).

Method 600 can continue at step 612, which includes circulating the sub-cooled portion of the liquid phase to an expansion device through the liquid line. For example, continuing the example of air conditioning system 100, sub-cooled refrigerant liquid 109 is circulated from the heat exchanger 112 to the throttling device 115 (through a conduit such as a copper tubing which is still considered a liquid line).

Method 600 can continue at step 614, which includes expanding the liquid phase of the refrigerant from a first pressure to a second pressure lower than the first pressure in the expansion device. For example, continuing the example of air conditioning system 100, as the sub-cooled refrigerant liquid 109 passes through the throttling device 115 (e.g., as a TXV), the liquid pressure drops rapidly, which also drops the temperature of the sub-cooled refrigerant liquid 109 rapidly. Thus, the temperature of refrigerant supply 121 is much lower than that of the sub-cooled refrigerant liquid 109.

Method 600 can continue at step 616, which includes circulating the liquid phase of the refrigerant at the second pressure to the evaporator. For example, continuing the example of air conditioning system 100, refrigerant supply 121 is circulated to the evaporator 120.

Method 600 can continue at step 618, which includes transferring heat from an airflow circulated through the evaporator to the liquid phase of the refrigerant at the second pressure to change at least a portion of the liquid phase of the refrigerant at the second pressure to the vapor phase of the refrigerant and change at least a portion of water vapor in the airflow into the liquid condensate. For example, continuing the example of air conditioning system 100, as refrigerant supply 121 passes through the evaporator 120 (e.g., through copper tubes mounted within aluminum fins to create heat transfer surfaces), heat from warm (return) airflow 124 that is blown (by a fan) across the evaporator 120 is transferred to the refrigerant supply 121. A cooled (supply) airflow 126 leaves the evaporator 120 and is provided to an indoor environment (where it absorbs heat from that environment to cool the indoor space). As heat is transferred from the warm (return) airflow 124, water vapor entrapped in the warm airflow condenses (as the air approaches its psychrometric saturation point). The now condensed water vapor is captures as condensate 114 (i.e., water) in the condensate pan 130 of the evaporator 120.

As the refrigerant supply 121 gains heat from the airflow, the supply 121 (as a liquid) boils off (or evaporates) into the low pressure refrigerant vapor 102 (refrigerant return), which is circulated back to the compressor 105 (to start the cycle over again). As described, in some aspects, a pressure bulb 125 measures a quality, or superheat, of the low pressure refrigerant vapor 102 as it returns to the compressor 105 in order to control the operation of the throttling device 115 (as a TXV).

A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. For example, example operations, methods, or processes described herein may include more steps or fewer steps than those described. Further, the steps in such example operations, methods, or processes may be performed in different successions than that described or illustrated in the figures. Accordingly, other implementations are within the scope of the following claims. 

What is claimed is:
 1. An air conditioning system, comprising: at least one compressor configured to compress a refrigerant in a vapor phase; a condenser fluidly coupled to the at least one compressor to receive the compressed vapor phase of the refrigerant and configured to change the compressed vapor phase of the refrigerant to a liquid phase of the refrigerant by transferring heat from the compressed vapor phase of the refrigerant to a cooling fluid; an expansion device fluidly coupled to the condenser with a liquid line to receive the liquid phase of the refrigerant and configured to expand the liquid phase of the refrigerant from a first pressure to a second pressure lower than the first pressure; an evaporator fluidly coupled to the expansion device to receive the liquid phase of the refrigerant at the second pressure and configured to transfer heat from an airflow circulated through the evaporator to the liquid phase of the refrigerant at the second pressure to change at least a portion of the liquid phase of the refrigerant at the second pressure to the vapor phase of the refrigerant and change at least a portion of water vapor in the airflow into a liquid condensate; and a heat exchanger fluidly coupled to the liquid line to receive at least a portion of the liquid phase of the refrigerant from the condenser upstream of the expansion device, the heat exchanger at least partially immersed in the liquid condensate captured in a condensate receiver from the evaporator and configured to sub-cool the portion of the liquid phase of the refrigerant based on a transfer of heat from the portion of the liquid phase of the refrigerant to the liquid condensate.
 2. The system of claim 1, wherein the heat exchanger is integral with and part of the liquid line.
 3. The system of claim 2, wherein the heat exchanger comprises a plurality of loops that are immersed in the liquid condensate captured in the condensate receiver from the evaporator.
 4. The system of claim 3, wherein the evaporator comprises a cooling coil that comprises a plurality of tubing rows, and the plurality of loops comprise a subset of the plurality of tubing rows.
 5. The system of claim 1, wherein the heat exchanger comprises a shell-and-tube heat exchanger at least partially immersed in the liquid condensate captured in the condensate receiver from the evaporator.
 6. The system of claim 5, wherein the shell-and-tube heat exchanger comprises: a condensate inlet fluidly coupled to the liquid condensate in the condensate receiver; a condensate outlet fluidly coupled to an outlet of the condensate receiver; a liquid refrigerant inlet fluidly coupled to the condenser through the liquid line; and a liquid refrigerant outlet fluidly coupled to the expansion device through the liquid line.
 7. The system of claim 5, further comprising a pump positioned to circulate liquid condensate to the shell-and-tube heat exchanger and through the condensate inlet.
 8. The system of claim 5, wherein the shell-and-tube heat exchanger comprises a heat exchange surface configured to transfer heat from the liquid phase of the refrigerant to the liquid condensate.
 9. The system of claim 1, wherein the heat exchanger comprises a liquid refrigerant inlet directly fluidly coupled to an outlet the condenser and a liquid refrigerant outlet directly coupled to an inlet of the expansion device.
 10. The system of claim 9, further comprising a valve positioned in the liquid line between the liquid refrigerant inlet and the liquid refrigerant outlet.
 11. The system of claim 10, wherein the valve comprises a solenoid valve.
 12. The system of claim 1, wherein the refrigerant comprises a non-natural refrigerant.
 13. The system of claim 12, wherein the non-natural refrigerant comprises at least one hydrofluorocarbon (HFC) refrigerant.
 14. The system of claim 13, wherein the at least one HFC refrigerant comprises a blend of two or more HFC refrigerants.
 15. The system of claim 13, wherein the at least one HFC refrigerant comprises at least one of HFC-134a, HFC-404a, HFC-410a, or HFC-407c.
 16. The system of claim 1, wherein the cooling fluid comprises a cooling airflow circulated through the condenser by at least one fan to transfer heat from the vapor phase of the refrigerant to the cooling airflow.
 17. The system of claim 1, wherein the heat exchanger comprises a liquid-to-liquid heat exchanger, the system further comprising a liquid-to-air heat exchanger positioned to receive at least a portion of the airflow that exits the evaporator and the portion of the liquid phase of the refrigerant from the condenser upstream of the liquid-to-liquid heat exchanger, the liquid-to-air heat exchanger configured to transfer heat from the portion of the liquid phase of the refrigerant to the portion of the airflow that exits the evaporator.
 18. The system of claim 17, wherein the liquid-to-air heat exchanger comprises a first liquid-to-air heat exchanger, the system further comprising a second liquid-to-air heat exchanger positioned to receive at least a portion of the airflow that enters the evaporator and the portion of the liquid phase of the refrigerant from the first liquid-to-air heat exchanger upstream of the liquid-to-liquid heat exchanger, the second liquid-to-air heat exchanger configured to transfer additional heat from the portion of the liquid phase of the refrigerant to the portion of the airflow that enters the evaporator.
 19. The system of claim 1, wherein the heat exchanger comprises a liquid-to-liquid heat exchanger, the system further comprising a liquid-to-air heat exchanger positioned to receive at least a portion of the airflow that enters the evaporator and the portion of the liquid phase of the refrigerant from the condenser upstream of the liquid-to-liquid heat exchanger, the liquid-to-air heat exchanger configured to transfer heat from the portion of the liquid phase of the refrigerant to the portion of the airflow that enters the evaporator.
 20. A method for sub-cooling a refrigerant in an air conditioning system, comprising: compressing a refrigerant in a vapor phase with at least one compressor; circulating the compressed vapor phase of the refrigerant from the at least one compressor to a condenser; changing the compressed vapor phase of the refrigerant to a liquid phase of the refrigerant in the condenser by transferring heat from the compressed vapor phase of the refrigerant to a cooling fluid; circulating at least a portion of the liquid phase of the refrigerant from the condenser through a liquid line to a heat exchanger that is at least partially immersed in a liquid condensate captured in a condensate receiver of an evaporator; sub-cooling the portion of the liquid phase of the refrigerant in the heat exchanger; circulating the sub-cooled portion of the liquid phase to an expansion device through the liquid line; expanding the liquid phase of the refrigerant from a first pressure to a second pressure lower than the first pressure in the expansion device; circulating the liquid phase of the refrigerant at the second pressure to the evaporator; and transferring heat from an airflow circulated through the evaporator to the liquid phase of the refrigerant at the second pressure to change at least a portion of the liquid phase of the refrigerant at the second pressure to the vapor phase of the refrigerant and change at least a portion of water vapor in the airflow into the liquid condensate.
 21. The method of claim 20, wherein the heat exchanger is integral with and part of the liquid line.
 22. The method of claim 21, further comprising circulating the portion of the liquid phase through a plurality of loops of the heat exchanger that are immersed in the liquid condensate captured in the condensate receiver from the evaporator.
 23. The method of claim 21, wherein the evaporator comprises a cooling coil that comprises a plurality of tubing rows, and the plurality of loops comprise a subset of the plurality of tubing rows.
 24. The method of claim 20, further comprising circulating the portion of the liquid phase through a shell-and-tube heat exchanger at least partially immersed in the liquid condensate captured in the condensate receiver from the evaporator.
 25. The method of claim 24, further comprising: circulating liquid condensate from the condensate receiver through the shell-and-tube heat exchanger; transferring heat from the portion of the liquid phase of the refrigerant to the liquid condensate in the shell-and-tube heat exchanger to sub-cool the portion of the liquid phase of the refrigerant and heat the liquid condensate; circulating the sub-cooled portion of the liquid phase of the refrigerant through the liquid line to the expansion device from the shell-and-tube heat exchanger; and circulating the heated liquid condensate to a drain of the condensate receiver.
 26. The method of claim 25, wherein circulating liquid condensate from the condensate receiver through the shell-and-tube heat exchanger comprises circulating liquid condensate from the condensate receiver through the shell-and-tube heat exchanger with a pump in or adjacent the condensate receiver.
 27. The method of claim 20, further comprising circulating another portion of the liquid phase of the refrigerant through a valve positioned in the liquid line between the condenser and the expansion valve.
 28. The method of claim 27, wherein the valve comprises a solenoid valve.
 29. The method of claim 20, wherein the refrigerant comprises a non-natural refrigerant.
 30. The method of claim 29, wherein the non-natural refrigerant comprises at least one hydrofluorocarbon (HFC) refrigerant.
 31. The method of claim 30, wherein the at least one HFC refrigerant comprises a blend of two or more HFC refrigerants.
 32. The method of claim 30, wherein the at least one HFC refrigerant comprises at least one of HFC-134a, HFC-404a, HFC-410a, or HFC-407c.
 33. The method of claim 20, wherein the cooling fluid comprises a cooling airflow, the method further comprising circulating the cooling airflow through the condenser by at least one fan to transfer heat from the vapor phase of the refrigerant to the cooling airflow.
 34. The method of claim 20, wherein the heat exchanger comprises a liquid-to-liquid heat exchanger, the method further comprising: circulating the portion of the liquid phase of the refrigerant from the condenser to a liquid-to-air heat exchanger prior to circulating the portion of the liquid phase of the refrigerant to the liquid-to-liquid heat exchanger; circulating at least a portion of the airflow that exits the evaporator through the liquid-to-air heat exchanger; transferring heat from the portion of the liquid phase of the refrigerant to the portion of the airflow that exits the evaporator in the liquid-to-air heat exchanger; and circulating the cooled portion of the liquid phase of the refrigerant from the liquid-to-air heat exchanger to the liquid-to-liquid heat exchanger.
 35. The method of claim 34, wherein the liquid-to-air heat exchanger comprises a first liquid-to-air heat exchanger, the method further comprising: circulating the cooled portion of the liquid phase of the refrigerant from the first liquid-to-air heat exchanger to a second liquid-to-air heat exchanger prior to circulating the portion of the liquid phase of the refrigerant to the liquid-to-liquid heat exchanger; circulating at least a portion of the airflow that enters the evaporator through the second liquid-to-air heat exchanger; transferring heat from the cooled portion of the liquid phase of the refrigerant to the portion of the airflow that enters the evaporator in the second liquid-to-air heat exchanger; and circulating the further cooled portion of the liquid phase of the refrigerant from the second liquid-to-air heat exchanger to the liquid-to-liquid heat exchanger.
 36. The method of claim 20, wherein the heat exchanger comprises a liquid-to-liquid heat exchanger, the method further comprising: circulating at least a portion of the liquid phase of the refrigerant from the condenser to a liquid-to-air heat exchanger prior to circulating the portion of the liquid phase of the refrigerant to the liquid-to-liquid heat exchanger; circulating at least a portion of the airflow that enters the evaporator through the liquid-to-air heat exchanger; transferring heat from the portion of the liquid phase of the refrigerant to the portion of the airflow that enters the evaporator in the liquid-to-air heat exchanger; and circulating the cooled portion of the liquid phase of the refrigerant from the liquid-to-air heat exchanger to the liquid-to-liquid heat exchanger. 